Dispersal of the environmental weed Bridal Creeper, Asparagus asparagoides, by Silvereyes, Zosterops lateralis, in south-western Australia

Abstract

The diffusion of the environmental weed Bridal Creeper, Asparagus asparagoides, was investigated in south-western Australia. The primary aim was to identify native passerines dispersing the weed and to determine whether the weed’s current density distribution was correlated to the flight patterns of dispersal agents. The secondary aim was to test whether modelling techniques developed for assessing the diffusion of animal pests and diseases were suitable for estimating diffusion of a bird-dispersed environmental weed. Diffusion of A. asparagoides in south-western Australia mostly involved the Silvereye, Zosterops lateralis. Over 60% of weed distribution records with the greatest density were less than 50 m from source infestations. Gut passage rates of Z. lateralis and estimates of its flight speed showed that the maximum potential dispersal distance was approximately 12 km. Modelling showed significant differences between dispersal curves generated from current weed density distribution records (c. 77 m) and those generated from Z. lateralis flight pattern data (c. 90 m). Differences may have resulted from weed distribution/density maps not taking into account dispersal beyond the boundaries of fragmented habitats. The distribution of habitats favoured by Z. lateralis may influence the pattern of diffusion and rate of spread of the weed.